He wasn’t supposed to do it, but on May 15, 1948, Lieutenant Colonel Paul H. Fackler, commanding officer of the U.S. Air Force 514th Reconnaissance Squadron Weather, flew his airplane into the seething mushroom cloud of an atomic bomb detonation. As part of Zebra, the final shot of America’s second series of atomic tests at Enewetak atoll in the Pacific, Fackler had the job of tracking the atomic cloud from at least 10 miles away, hoping that special filters attached to the airplane would catch samples of the radioactive debris. But as he pulled away from the enormous roiling cloud...